1. Field of the Invention
The present invention relates to controlling a power circuit, especially to controlling rush current occurring in a step-up circuit included in a power circuit.
2. Description of the Related Art
Some electronic machines have conventional power circuits including a plurality of voltage transforming circuits to change up or down the voltage applied by a common power source to various voltages.
Some methods for protecting electronic machines from rush current occurring when they start, are known. For example, the flow of rush current into an electronic machine is restrained by gradually applying the voltage to the electronic machine during the starting time.
However, if a voltage is gradually applied to the electronic machine, a circuit for controlling this rush current is necessary, therefore, the structure of the electronic machine should be complex. Further, in this case, operability of the electronic machine becomes low, because it takes a long time to start.
In a power circuit having a plurality of voltage transforming circuits, when rush current occurs in one of these voltage transforming circuits, other circuits are negatively impacted. That is, the voltage supplied by each voltage transforming circuit, becomes lower. In the step-down circuits for generating lower voltages than the voltage from the power source, to be provided to microcomputers and so on, this negative impact is more serious than in the step-up circuits. This is because the ratio of voltage drop against generated voltage is larger in step down circuits than in step-up circuits. Therefore, rush current can cause serious problems to loads such as microcomputers.